4-HYDROXY-4'-ISOPROPOXYDIPHENYL SULFONE DEVELOPER COMPOSITION, WET PULVERIZING METHOD, AND DISPERSION

Abstract: A method of preventing hydration of 4-hydroxy-4'-isopropoxydiphenyl sulfone characterized by wet pulverizing the sulfone in water in the presence of a diphenyl sulfone derivative represented by general formula (I): (wherein R¹ represents hydrogen or lower alkyl; R² and R³ represent each independently lower alkyl; and n and m represent each an integer of 0, 1 to 4, provided when R¹ is hydrogen, not both of m and n are 0 at the same time). A highly sensitive recording paper free from scumming can be produced by using a dispersion of a developer comprising the above sulfone.

Description: A composition for color development comprising 4-hydroxy-4'-isopropoxydiphenylsulfone, and a wet method for grinding and a dispersion for applying the same. Field of the Invention The present invention relates to 4-hydroxy-4'-isopropoxydiphenylsulfone which can function as a color developer to be used for the production of recording papers such as thermal sensitive recording papers. Background Art In the manufacture of thermal sensitive recording papers, a leuco chromogen and a color developer, which are both colorless or pale-colored, are normally coated on supporting materials such as papers. In the process for the manufacture of a coating solution for such a use, a color developer is dispersed into an aqueous solution of a water-soluble polymer being a binding agent to prepare the coating solution. Since thermal sensitive recording papers are required to have a property of high sensitivity to temperature, it is necessary to make a particle size of a color developer in the dispersion thereof as fine as possible in order to produce thermal sensitive recording papers having an excellent temperature-sensitivity. For this reason, most of dispersions of color developers wherein a color developer is grinded up to fine particles have been produced by adding the color developer into an aqueous solution of a water-soluble polymer and subsequently grinding them thoroughly by employing certain wet grinding methods. Although 4-hydroxy-4'-isopropoxydiphenylsulfone can function as an excellent color developer and is widely used, the compound sometimes crystallizes, either during the process of wet grinding to prepare a dispersion of the color developer or during the preservation of the dispersion of the color developer prepared, when the color developer was grinded up to fine particles by employing the means as described above. Particularly this phenomenon becomes more conspicuous when 4-hydroxy-4'-isopropoxydiphenylsulfone is grinded up to a particle size of less than 1 µm. It is understood that this formation of crystals is explained as a result of a hydration phenomenon of 4-hydroxy-4'-isopropoxydiphenylsulfone and the crystals formed at the hydrate of 4-hydroxy-4'-isopropoxydiphenylsulfone. This hydrate is seriously related to a disadvantageous property of thermal sensitive recording papers such as an unclean background, because the termal sensitive recording papers tend to result in uncleanlyness of the background of the recording papers when they are produced by using a dispersion of a color developer which contains such a hydrate. As a means for preventing the formation of said crystals (hydration), a method to add 4,4'-dihydroxydiphenylsulfone to 4-hydroxy-4'-isopropoxydiphenylsulfone to prevent the formation of crystals is disclosed in the Japanese patent laid-opened no. Hei 2-76779. By even employing this method for the production of thermal sensitive recording papers, however, the recording papers frequently give said unclean background when the adding rate of 4,4'-dihydroxydiphenylsulfone is raised to about 5%. It is an object of the present invention to provide an improved means for preventing said hydration of 4-hydroxy-4'-isopropoxydiphenylsulfone during the process of the production of a dispersion of color developer and during the storing thereof. Disclosure of the Invention It is an object of the present invention to provide a method for preventing the hydration of 4-hydroxy-4'-isopropoxydiphenylsulfone by contaminating therein a compound selected from a group consisting of diphenylsulfone derivatives represented by the general formula (I): wherein R 1 represents hydrogen or lower alkyl, R 2 and R 3 represent each independently lower alkyl, n and m denote 0 or an integer of from 1 to 4, with the proviso that n and m can never be 0 at the same time in case R 1 represents hydrogen or isopropyl, in an amount of 0.01 part by weight or more per 100 parts by weight of 4-hydroxy-4'-isopropoxydiphenylsulfone. It is a further object of the present invention to provide a composition for color development comprising 4-hydroxy-4'-isopropoxydiphenylsulfone which further contains a diphenylsulfone derivative represented by the general formula (I) as defined above and to provide a dispersion comprising said composition for color development. It is still a further object of the present invention to provide a wet method for grinding 4-hydroxy-4'-isopropoxydiphenylsulfone in water characterized in that the particles of 4-hydroxy-4'-isopropoxydiphenylsulfone are subjected to wet grinding in the presence of at least phenylsulfone are subjected to wet grinding in the presence of at least one compound selected from a group consisting of diphenylsulfone derivatives represented by the general formula (I) as defined above. The lower alkyl which can be exemplified for the substituents R 1 , R 2 and R 3 in diphenylsulfone derivatives represented by the general formula (I), are methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, etc.. Representative compounds for diphenylsulfone derivatives represented by the general formula (I) which contain the lower alkyl substituents as exemplified above are recited hereinbelow. In the examples of the representative compounds recited below, propyl and isopropyl are represented by isopropyl; n-butyl, isobutyl, sec-butyl and tert-butyl are altogether represented by n-butyl. 4-hydroxy-3-methyl-4'-isopropoxydiphenylsulfone 4-hydroxy-3-ethyl-4'-isopropoxydiphenylsulfone 4-hydroxy-3-isopropyl-4'-isopropoxydiphenylsulfone 4-hydroxy-3-n-butyl-4'-isopropoxydiphenylsulfone 4-hydroxy-3'-methyl-4'-isopropoxydiphenylsulfone 4-hydroxy-3'-ethyl-4'-isopropoxydiphenylsulfone 4-hydroxy-3'-isopropyl-4'-isopropoxydiphenylsulfone 4-hydroxy-3'-n-butyl-4'-isopropoxydiphenylsulfone 4-hydroxy-3-methyl-4'-methoxydiphenylsulfone 4-hydroxy-3-ethyl-4'-methoxydiphenylsulfone 4-hydroxy-3-isopropyl-4'-methoxydiphenylsulfone 4-hydroxy-3-isopropyl-4'-ethoxydiphenylsulfone 4-hydroxy-3-isopropyl-4'-butoxydiphenylsulfone 4-hydroxy-3-n-butyl-4'-methoxydiphenylsulfone 4-hydroxy-3,3'-dimethyl-4'-methoxydiphenylsulfone 4-hydroxy-2,2'-dimethyl-4'-isopropoxydiphenylsulfone 4-hydroxy-3,3'-dimethyl-4'-isopropoxydiphenylsulfone 4-hydroxy-3,3',5,5'-tetramethyl-4'-methoxydiphenylsulfone 4-hydroxy-3,3',5,5'-tetramethyl-4'-isopropoxydiphenylsulfone 4,4'-dihydroxy-2-methyldiphenylsulfone 4,4'-dihydroxy-2-ethyldiphenylsulfone 4,4'-dihydroxy-2-isopropyldiphenylsulfone 4,4'-dihydroxy-2-n-butyldiphenylsulfone 4,4'-dihydroxy-3-methyldiphenylsulfone 4,4'-dihydroxy-3-ethyldiphenylsulfone 4,4'-dihydroxy-3-isopropyldiphenylsulfone 4,4'-dihydroxy-3-n-butyldiphenylsulfone 4,4'-dihydroxy-3,3'-dimethyldiphenylsulfone 4,4'-dihydroxy-3,3'-diethyldiphenylsulfone 4,4'-dihydroxy-3,3'-diisopropyldiphenylsulfone 4,4'-dihydroxy-2,2'-dimethyldiphenylsulfone 4,4'-dihydroxy-2,2'-diethyldiphenylsulfone 4,4'-dihydroxy-2,2'-diisopropyldiphenylsulfone 4,4'-dihydroxy-2,2'-diisobutyldiphenylsulfone 4,4'-dihydroxy-3,3',5,5'-tetramethyldiphenylsulfone 4,4'-dihydroxy-3,3',5,5'-tetraethyldiphenylsulfone 4,4'-dihydroxy-3,3',5,5'-tetraisopropyldiphenylsulfone The content of the additional diphenylsulfone derivative represented by the general formula (I) in the dispersion is 0.01 part by weight or more per 100 parts by weight of 4-hydroxy-4'-isopropoxydiphenylsulfone. However, it is preferable that said content of the diphenylsulfone derivative is 0.05 part by weight or more in order to prevent the formation of the hydration of 4-hydroxy-4'-isopropoxydiphenylsulfone in the dispersion for color development prepared by wet grinding. Furthermore, it is required that said content of the diphenylsulfone derivative is 0.10 part by weight or more in order to ensure complete prevention of the formation of the hydration of 4-hydroxy-4'-isopropoxydiphenylsulfone in the dispersion for color development throughout the long-term preservation thereof. Although said preventing effect can be obtained as well when the content of the diphenylsulfone derivative is more than 1.0 part by weight, and even when more than 5.0 parts by weight, it will not give any further advantage for the property and is therefore uneconomic. Considering the practical use of the dispersion, it is preferable to fix the content in a range of from 0.05 to 1.0 part by weight, and more preferably in a range of from 0.1 to 0.6 part by weight per 100 parts by weight of 4-hydroxy-4'-isopropoxydiphenylsulfone. The diphenylsulfone derivative represented by the general formula (I) as defined above can be added to the reactant solution or to the crystals of 4-hydroxy-4'-isopropoxydiphenylsulfone, which precipitated during the manufacture of 4-hydroxy-4'-isopropoxydiphenylsulfone, in any form of powder or, alternatively, as a solution in a solvent. Furthermore, the diphenylsulfone derivative can be added to the dispersion of 4-hydroxy-4'-isopropoxydiphenylsulfone by adjusting the solution just before subjecting it to the wet grinding process. If 4-hydroxy-4'-isopropoxydiphenylsulfone is synthesized by the reaction of 4,4'-dihydroxydiphenylsulfone and isopropylbromide as by-product a diphenylsulfone derivative represented by the general formula (I) would be formed. In such a case, it is possible to leave the by-product and to utilize it as a diphenylsulfone derivative required for the addition described above and to further add a supplemental quantity of fresh diphenylsulfone derivative in case the amount of the by-product formed is not sufficient for obtaining the necessary preventive effect. When plural types of the diphenylsulfone derivatives represented by the general formula (I) are formed as by-products, all of the derivatives formed can be used in the same manner as described above. Although water is employed as a dispersing carrier for the wet grinding specified in the present invention, it is preferable to carry out the wet grinding in the presence of a dispersing agent in order to improve the dispersibility of 4-hydroxy-4'-isopropoxydiphenylsulfone in the dispersion. As dispersing agents described above, dispersing agents or surface active agents normally used can be employed. However, for the production of thermal sensitive recording papers, it is a common procedure to prepare a dispersion of a color developer in a state of fine particles by dispersing the color developer into a solution of a water-soluble polymer which is used as a binder and subjecting the resulting mixture to the subsequent wet grinding process. According to the present invention, it is also preferable to use said water-soluble polymer as a dispersing agent and then to proceed to the subsequent wet grinding process. For the water-soluble polymers, compounds to be used as binders for color developers such as polyvinyl alcohol, methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, polyacrylamide and starch, can be used. Among them, polyvinyl alcohol is the most common compound for such use. However, it is possible to add other additives normally used for a dispersion of a color developer into a dispersing carrier. The wet grinding method specified in the present invention does not require any particular conditions, so that normal wet grinding methods using ball mill, sand mill, etc. can be employed in the present invention. There is no particular requirement for the concentration range of 4-hydroxy-4'-isopropoxydiphenylsulfone in the composition for color development when it is subjected to the wet grinding, and therefore the wet grinding can be operated at any concentration of 4-hydroxy-4'-isopropoxydiphenylsulfone as far as the concentration is adequate for a coating solution used for the production of thermal sensitive recording papers. The formation of the hydrates can be determined by several means, such as IR spectroscopy, differential thermal analysis, etc.. On the other hand, microscopic observation in the dispersion can be utilized as a simple method for the determination, since the crystals of 4-hydroxy-4'-isopropoxydiphenylsulfone grow too fast and large crystals and become visible when the hydration of the particles thereof is going on. Preferred embodiment for carrying out the present invention Now, the present invention is further explained in detail by the examples. However, the scope of the present invention shall not be limited to the descriptions in the following examples. Example 1 31.1 g of 15% aqueous solution of polyvinyl alcohol, 30 g of pure water, 195 g of glass beads (1.0-1.5mm ⊘), 13.9 g of 4-hydroxy-4'-isopropoxydiphenylsulfone and 0.14 g of 4-hydroxy-3-isopropyl-4'-isopropoxydiphenylsulfone (adding ratio: 0.10% by weight) were each weighed and mixed altogether, then the mixture was subjected to wet grinding at 25°C by using a wet grinder (manufactured by Igarashi Machinery Manufacturing Co., Ltd.; trade name, Sandgrinder). On microscopic observation, formation of crystals in the mixture was observed after 3 hours from the start of the wet grinding. The average particle size in the mixture after the wet grinding was 0.5 µm according to the measurement by using a laser diffraction-type particle size distribution analyzer (Shimazu Particle Size Distribution Analyzer SALD-1000, at 50% average particle size). Example 2 By employing the same procedure as described in the example 1 except the replacement of the dose of 4-hydroxy-3-isopropyl-4'-isopropoxydiphenylsulfone from 0.14 g (adding ratio: 0.10% by weight) to 0.28 g (adding ratio: 0.20% by weight), wet grinding was carried out. On microscopic observation, no formation of crystals was detected in the mixture even after 10 hours from the start of the wet grinding. The average particle size in the mixture after the wet grinding was 0.3 µm according to the measurement by using the same method described in the example 1. Example 3 By employing the same procedure as described in the example 2 except the replacement of 4-hydroxy-3-isopropyl-4'-isopropyldiphenylsulfone by 4,4'-dihydroxy-3-isopropyldiphenylsulfone, wet grinding was carried out. On microscopic observation, no formation of crystals was detected in the mixture even after 10 hours from the start of the wet grinding. The average particle size in the mixture after the wet grinding was 0.0 µm according to the measurement by using the method described in the example 1. Comparative Example With no addition of the compound of the present invention, wet grinding was carried out according to the same procedure as described in the example 1. On microscopic observation, formation of crystals was clearly observed in the mixture after 1 hour from the start of the wet grinding. The average particle size in the mixture after the wet grinding was 0.8 µm according to the measurement by using the same method described in the example 1. Incidentally, in the example 1 above, the average particle size in the grinded mixture after 1 hour was 0.5 µm. Industrial Applicability The sensitivity of thermal sensitive recording papers and carbonless papers is made finer. According to the present invention, a dispersion comprising 4-hydroxy-4'-isopropoxydiphenylsulfone in a state of very fine particles can be easily prepared, because the present invention enables the wet grinding by which such fine particles of 4-hydroxy-4'-isopropoxydiphenylsulfone can be made to an average particle size of less than 1 µm without causing the hydration of the compound and the particles grinded to not form the hydrate in the dispersion prepared either. Therefore, the production of high sensitive and unclean background-free thermal sensitive recording papers can be accomplished by using the dispersion of color developer according to the present invention.

Claims: A composition for color development containing 4-hydroxy-4'-isopropoxydiphenylsulfone, characterized in that the composition further contains one or more diphenylsulfone derivatives represented by the general formula (I): wherein R 1 represents hydrogen or lower alkyl, R 2 and R 3 represent each independently lower alkyl, n and m denote 0 or an integer of from 1 to 4, with the proviso that n and m can never be 0 at the same time in case R 1 represents hydrogen or isopropyl, in an amount in total ranging from 0.05 to 5.0 parts by weight or more per 100 parts by weight of 4-hydroxy-4'-isopropoxydiphenylsulfone. The composition according to claim 1, characterized in that the content of said diphenylsulfone derivatives is in a range of from 0.05 to 1.0 parts by weight per 100 parts by weight of 4-hydroxy-4'-isopropoxydiphenylsulfone. A method for grinding 4-hydroxy-4'-isopropoxydiphenylsulfone without forming the hydration product thereof in a dispersing carrier, wherein the particles of 4-hydroxy-4'-isopropoxydiphenylsulfone are subjected to a wet grinding process in the presence of one or more diphenylsulfone derivatives represented by the general formula (I): wherein R 1 represents hydrogen or lower alkyl, R 2 and R 3 represent each independently lower alkyl, n and m denote 0 or an integer of from 1 to 4, with the proviso that n and m can never be 0 at the same time in case R 1 represents hydrogen or isopropyl, in an amount ranging from 0.05 to 5.0 parts by weight per 100 parts by weight of 4-hydroxy-4'-isopropoxydiphenylsulfone. An aqueous solution of a water-soluble polymer in which the composition for color development according to claim 1 is dispersed.

Inventors: HIDAKA TOMOYA, SATO HIROYASU, SATO SHINICHI, TAKASHINA YUTAKA, HIDAKA, TOMOYA, SATO, HIROYASU, SATO, SHINICHI, TAKASHINA, YUTAKA, HIDAKA, Tomoya R &amp; D Lab. for Specialty Chemicals, SATO, Shinichi R &amp; D Lab. for Specialty Chemicals
Applicants: NIPPON SODA CO, NIPPON SODA CO., LTD.
Application year: 1994
Main classification: B41M5
IPC codes: B41M5, C07C317, C07C315